Metamaterial
A metamaterial ( 400 ) for attenuating acoustic transmission comprises a plurality of layers ( 410 ). Each layer ( 410 ) comprises a transmission structure ( 420 ) and a resonator ( 450 ), coupled to the transmission structure ( 420 ). The transmission structure ( 420 ) in a layer ( 410 ) is coupled to the transmission structures ( 420 ) of the layers ( 410 ) neighboring said layer ( 410 ). The resonator ( 450 ) in a layer ( 410 ) is coupled to the transmission structure ( 420 ) of the layers ( 410 ) neighboring said layer ( 410 ).
1. A metamaterial for attenuating acoustic transmission, the metamaterial comprising a plurality of layers, each layer comprising:
(a) a transmission structure, and
(b) a resonator, coupled to the transmission structure,
wherein the transmission structure in a layer is coupled by a coupling element to the transmission structures of the layer(s) neighboring said layer; wherein the resonator in a layer is coupled by a coupling element to the transmission structure of the layer(s) neighboring said layer.
2. A metamaterial as claimed in claim 1 , in which there are at least three of said layers.
3. A metamaterial as claimed in claim 1 , in which the transmission structure comprises a disc or an annulus.
4. A metamaterial as claimed in claim 3 , in which the discs or annuli of the layers are coaxial with each other.
5. A metamaterial as claimed in claim 1 , in which the resonator is a cylinder.
6. A metamaterial as claimed in claim 5 , in which the cylinders of the layers are coaxial with each other.
7. A metamaterial as claimed in claim 6 , in which the transmission structure comprises a disc or an annulus and the cylinders are co-axial with the discs or annuli.
8. A metamaterial as claimed in claim 1 , in which any of the couplings are viscoelastic couplings.
9. A metamaterial as claimed in claim 1 , in which the metamaterial includes at least one active element configured to enhance the attenuation of acoustic transmission.
10. A metamaterial as claimed in claim 9 , in which the at least one active element is comprised in at least one of the resonators.
11. A metamaterial as claimed in claim 9 , in which the active element is configured to enhance the attenuation of acoustic transmission by control of reactive forces between resonator elements.
12. A metamaterial as claimed in claim 9 , in which the active element is configured to apply a point force to the resonator.
13. A metamaterial as claimed claim 9 , in which the active element is configured to enhance the attenuation of acoustic transmission according to an optimization algorithm.
14. A metamaterial as claimed in claim 13 , in which the optimization algorithm minimizes the movement of an element of a layer at a first end of the layers in response to movement of an element of a layer at a second, opposite, end of the layers.
15. A method of manufacturing a metamaterial, the method comprising manufacturing the metamaterial of claim 1 by a three-dimensional printing technique.